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Author Topic: Proper fastener hardware for antennas in coastal environment?  (Read 1920 times)
KT5MR
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« on: December 26, 2015, 11:08:33 AM »

Hi all,

I'm working on replacing/re-doing some of my wire antennas that I put up when I was first licensed.  At the time, I really didn't pay attention to the screws, bolts, and nuts I used in their construction. 

As I live along the Texas Gulf Coast (90% humidity, 78 degrees F on Christmas Eve!), all of the fasteners have rusted substantially.  I suspect most of these were simply zinc-plated.  (Some fasteners which I thought were stainless steel also have rusted, but these also were submerged in water in some of our heavy rain this year.  Or maybe they simply weren't stainless as the cheap SO-239 to which they are attached is just fine.)

Is stainless steel hardware okay or should I seek out full galvanized?  What about black-oxide coating?  I'm having trouble finding 4-40 screws locally for the Amphenol SO-239's I bought and Home Depot has it on order, but it is black-oxide coated, which some web searches suggest is an insulator.

--Michael / KT5MR

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KE6EE
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« Reply #1 on: December 26, 2015, 11:40:00 AM »


As I live along the Texas Gulf Coast (90% humidity, 78 degrees F on Christmas Eve!), all of the fasteners have rusted substantially.  


It's not just the humidity in a marine environment. Here on the West Coast within several miles of the coast, or in my case, San Francisco Bay, there's also salt in the air. No doubt the same where you are. Cars rust from the top down rather than from the bottom up in the as they do in the snowbelt where roads are cleared with salt. Unprotected metals and some types of stainless steel corrode quickly.

I use stainless steel fasterners with the appropriate alloy for corrosive environments. Fasteners I've gotten in antenna components from DX Engineering have fared well. Random-quality stainless from the local hardware store not-always-well.

For some projects I've used high-quality heavily galvanized bolts, washers and nuts from a local hardware store and they are good. Zinc fasteners rust quickly.

I have a couple of commercially-made baluns (placed outside) with stainless wire-terminal bolts. The star lockwashers  which came with them have rusted a bit although the bolts and flat washers are fine. On a DX Engineering balun there are split lockwashers which have not rusted.

Bottom line is that you need to use the appropriate quality of "corrosion free" fasteners.

« Last Edit: December 26, 2015, 11:43:09 AM by KE6EE » Logged
KT5MR
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Posts: 25




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« Reply #2 on: December 26, 2015, 03:15:01 PM »

Thanks for the advice, Michael.

And especially for the DX Engineering reference.  I never thought to check there!  As it turns out, they have a complete stainless steel 4-40 mounting kit for $2.95 (http://www.dxengineering.com/parts/dxe-fsm-hwk) for the Amphenol SO-239s.  That will save me some time and money.

--Michael / KT5MR
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KS2G
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« Reply #3 on: December 26, 2015, 03:40:13 PM »

As I live along the Texas Gulf Coast...

You probably can find what you need (with good advice about corrosion resistance) at a marine (boating) supply store.

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WA7PRC
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« Reply #4 on: December 26, 2015, 03:40:39 PM »

Not all SS is the same. Corrosion resistance is related to the content of Chromium, as explained here: http://en.wikipedia.org/wiki/Stainless_steel
Some commonly-available alloys (such as 316) are considered better at resistance to corrosion. Others, not so much.
McMaster-Carr has a nice chart of SS alloys and their properties (link).

McMaster-Carr also has a very good selection of hardware. A few years ago, got tired of having a catch-as-catch-can hardware supply, and bought A LOT of SS hardware from them.

vy 73 es gl,
Bryan WA7PRC
« Last Edit: December 26, 2015, 03:43:40 PM by WA7PRC » Logged
N7BMW
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« Reply #5 on: December 27, 2015, 04:11:18 AM »

Even Marine store stainless is the 304 alloy.  316 is far superior in terms of corrosion resistance but is a bit weaker. 

Unfortunately stainless in contact with aluminum in a salt air environment causes electrolysis with the aluminum corroding.  In this environment an anti corrosion coating under each screw is important.  In the marine environment I have used two products that are very effective at eliminating electrolysis.  Tefgel and Duralaq.  Tefgel is grease like and does not harden, Duralaq will harden over time.  I say this because in a high vibration area Tefgel allows bolts to loosen - an issue on sailboats but probably not an issue on antennas. 

The best place to buy these is at a marine rigging supply.  Do not buy at West Marine - they sell (did sell?) a knock off of Tefgel that is a poor substitute. 
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KM1H
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« Reply #6 on: December 27, 2015, 07:08:50 AM »

+1 for a marine supplier. Im about 20-25 miles from the ocean in about a 120 degree arc and on top of the highest hill in the area (I can see Boston Harbor from the 180' tower) and regularly get salt laden fog as well as from any storm blowing in from the ocean. There are a few of the larger suppliers in NH, and MA that arent rip off price gougers that carry everything from SS hardware to  wire rope. Ive no idea what grade it is but some has been up for over 25 years and is still as new.

What makes it even worse is all the acid rain from the Midwest coal fired power plants which can strip off the tower and guy wire galvanizing.

Carl
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KT5MR
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« Reply #7 on: December 27, 2015, 08:16:36 AM »

Thanks for the advice all.  Had no idea there was as much to stainless steel as there is.  Smiley

I'm about 25 miles inland so we get a decent but not terrible amount of fog at times.  Most of the time it is just the ever-present humidity and the constant overnight dew....so while things aren't submerged in water, they are nearly always covered by a thin layer of moisture for about six hours a night at least.

73,

--Michael / KT5MR
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PA1ZP
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Posts: 480




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« Reply #8 on: December 27, 2015, 08:46:37 AM »

Hi

Bolts, nuts marked as A2 are 304 overhere in EU
Bolts, nuts marked A4 are 316.

How about expensive throwing away a $1000 to a new rig and do not want to pay for 4 little bolts and nuts and washers for SO239 for $3.

I even build my entire VHF 10 element beams (145 MHz) from stainless steel only 15 pounds of the stuff for each beam.

I always use stainless, but not where the extra money isn't worth the efford or weight will be a problem.
In my aluminium antennas I use galvanised (zinc) clamps as my antenna does need maintainance every 2 yrs and gets demounted and cleaned and if needed new clamps and bolts.

About corrosion between stainless and Alu , I found out that galvanised (zinc) did even corode far more and agressive on aluminium.

And it is useless to put for $20 clamps on a $2 antenna hihi.

I can reach all my antennas very easy and have all parts in spare tubes, wires, insulators, nuts, clamps, SO239 and bolts etc.

I had times I even had completely ready built and adjusted demounted antennas in spare, just had to change one antenna for another new one and after mounting and raising just repair and revise the other antenna with new parts and put it in spare again.
Or what happened far more often revise and give it away to another ham.

By the way all my antennas are homebrew, often threw away antennas as I just wanted something else.

rule 1 for antenna building: antennas, rotors, feedlines, towers need adjusting and maintenance, make sure that you can lower them reach them yourself easy and cheap, if you can not you have designed it the wrong way.

73 Jos
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K6UJ
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Posts: 734




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« Reply #9 on: December 28, 2015, 10:44:29 AM »

I would recommend only using 316SS.   I have found that 304SS will rust.   
I used to have rust issues with my antenna hardware and wasn't aware that 304SS would rust.
Now I only use 316SS and zero rust problems.

73,
Bob
K6UJ
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WA7PRC
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« Reply #10 on: December 28, 2015, 11:51:13 AM »

I would recommend only using 316SS.   I have found that 304SS will rust.   
I used to have rust issues with my antenna hardware and wasn't aware that 304SS would rust.
Now I only use 316SS and zero rust problems.

73,
Bob
K6UJ
The link I provided in post #4 above confirms the difference in corrosion resistance between 304 and 316, and many other alloys. Again, the difference is directly related to the percentage of Chromium, as I pointed out and referenced.

vy 73 es gl,
Bryan WA7PRC
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